Signaling system



Sept. 22, 1942- A. E. MELHOSE I SIGNALING SYSTEM Filed Aug. 51, 1940 4 Sheets-Sheet 1 QMQ 838 CB Q35 235 lNVE/VTOR 14. E MEL/I055 By j A A TTORNEV Sept. Z2,'1942. A MELHQSE 2,296,362

SIGNALING SYSTEM iled/m 51, 1940 4 SheetS -Shee t E A T TORNE Y P 1942- I A. E. MELHOSE 2,296,362

S IGNALING S'YSTEM Filed Aug. 31, 1940 I 4 Sheets-Sheet 3 TEL sakno :E I M fi l ld mun/2E0 7 POLAR/ZED Malv INVENTOR AEMELHOSE A T TORNEV A. E. MELHOSE SIGNALING SYSTEM FiledAL lg. 51, 1940 4 Sheets-Sheet 4 FIG. 4

CONTROL TELEGRAPH TELEGRAH CON TROL TO NE TONE TONE TONE UNSPREAD w UNSPREAD SPREAD SPREAD UNSPREAD SPREAD CHANNEL CHANNEL USED USED awe-200 T 0 freyuency 2295- 4590 50g'! I 2s 0o- 5000--- 4. 5909 01 RR/ER WAVE L ENG TH 0F ASSIGNED CHANNEL L /M/ TS OF- CHANNEL 1 lb K/LOCVCLES uv VEN TOR A. E MEL HOSE ATTORNFV Patented Sept. 22, 1942 SIGNALING SYSTEM Alfred E. Melhose, Westfield, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application August 31, 1940, Serial No. 354,987

9 Claims.

This invention relates to communication systems and particularly to systems where a first type of transmission is interpolated in a second type of transmission during lulls and pauses in such second type of transmission.

The object of the invention is to provide flexibility in the form of adjusting means to meet varying service conditions. cific embodiment of the invention an interpolated telephone and telegraph system is shown wherein telegraph signals are interpolated in telephone conversations during lulls and pauses in such conversation. The transmission is by Way of carrier current, it being immaterial whether the link is a radio channel or otherwise, though it is here shown as the former,

In carrier current transmission a space of some 10 kilocycles is generally allowed, this being about kilocycles on each side of the carrier frequency. It has been found that this kilocycle band may be divided in four parts and that itis feasible to use these four parts as four communication channels. There are thus two channels on each side of the carrier, each aproximately 2.5 kilocycles wide, one close to the carrier and the other 2.5 kilocycles distant. The channel next the carrier provides a band of speech frequencies of from 200 cycles to about 2750 cycles while the distant channel provides a band of from 2750 to 5000 cycles. To transmit over the outside or distant band requires an additional modulation which is well known and fully explained in Patent No. 1,502,889 to Van der Bijl.

In the system herein disclosed it is proposed to employ two of these four possible channels, one close to and on one side of the carrier, the other distant from and on the other side of the carrier. For the purpose of telegraph transmission and switching control, certain alternating currents of frequencies within or near the band of speech frequencies are employed. Thus a control tone which is transmitted with speech for switching purposes is just outside the band of speech frequencies so that it may be filtered out after it has performed its proper function. In addition, a telegraph tone which is transmitted at times occurring in lulls and pauses in speech and over circuits peculiarly adapted to the transmission of speech is within the band of speech frequencies. These may be spoken of as the fixed signaling currents.

When the speech band on one side of and close to the carrier is being used, the control tone may be of 3000 cycles and the telegraph tone may be In a preferred speing used these figures must be changed, the control tone to 5250 cycles and the telegraph tone to 4590 cycles so that there will be no interference with the twin channel which might be in use for some other purpose. By the same token the circuits affected by these tones must be changed.

A feature of the invention, therefore, is adjustable means at each terminal of the system for simultaneously changing thereat the frequencies of the fixed signaling currents and the frequency characteristics of the circuits affected thereby.

This invention is an improvement in the sys-, tem disclosed in Patent 2,207,720 granted to Cole et al. July 16, 1940.

The drawings consist of four sheets of diagrams. With Figs. 1, 2 and 3 placed together a circuit diagram of one terminal of an interpolated telephone and telegraph System is shown.

Fig. 1 shows the transmitting telegraph circuits;

Fig. 2, partly schematic and partly circuit diagram, shows the telephone and controlling circuits;

Fig. 3 shows the receiving telegraph circuits;

Fig. 4 is a diagram illustrating how the assigned channel with its carrier wave and both side-bands may be utilized for twin channel purposes.

In order to clearly understand the present invention the diagram of Fig. 4 will first be explained. A centrally located vertical line 400 indicates the carrier frequency of an assigned channel. Usually these channels are about 10 kilocycles wide with a side-band of 5 kilocycles extending to each side. The vertical line 40], therefore, indicates the limit in one direction and the vertical line 402 indicates the limit in the other direction. For practical purposes intelligible speech may be included in the band of about 2500 cycles, that is one-quarter of the width of this assigned channel. Theoretically, it is possible, therefore, to divide this 10-kilocycle band into four parts and to use these four parts for four separate speech channels. Practically, there are some difficulties involving cross-talk and other interference phenomenon which at present prevent the full use of the channel in this manner. However, it is entirely practical at the present time to use one chanel near to and on one side of the carrier wave for a speech channel and another channel distant from and on the other side of the carrier wave for a speech channel. The vertical lines 403 and 404 define the speech channel on one side of and near to the carrier of 2295 cycles, but when the other channel is bewave and the vertical lines 405 and 106 define the other channel distant from and on the other side of the carrier wave.

In the interpolated telephone and telegraph system it is necessary to send certain alternating current waves for control purposes. During the sending of speech a control tone which is just outside the speech band is sent with speech and during the times that speech is not present a telegraph tone within the speech band is transmitted. The vertical line 401 represents a control tone and the vertical line 468 represents a telegraph tone.

When the other of the twin channels is used it is necessary to shift the frequencies of these control tones and hence the tonerepresented by. the line 6-3! is shifted to the tone represented-by the line 4% and the telegraph tone represented by the line 498 is shifted to the frequency represented by the line 4H].

It will be understood that the various frequency designations on this diagram are purely by way of example and that other figures may with equal facility be employed. It will further be understood that if the line 459, which is slightly outside the assigned channel, is objectionable, then the same pattern may be used but a carrier wave shifted slightly toward the left may be employed so that the entire diagram will be within the assigned channel,

The term spread and unspread are employed by workers in this art to designate the two channels thus created. The unspread channel is that channel which is near to and on one side of the carrier frequency and the spread channel is that channel which is distant from and on the other side of the carrier frequency. The spread channel requires an additional modulation but since this means is well known in the art it will not further be explained at the present time.

Referring to the details of the speech control circuits, one terminal of a system is shown, but it will be understood that at some distant point a similar terminal is located, so that speech coming in over channel 2M will be transmitted from the radio transmitter 292 and its antenna 203, to be received at the said distant point over the antenna 204 and the radio receiver 295 for transmission into the speech path at that point correspondingto the channel 201.

While speech is being transmitted from channel 29'! over the antenna 263 the telegraph transmitti'ng apparatus of Fig. 1 is inactive and the telegraph receiving apparatus of Fig. 3 at the distant point is similarly inactive. By the same token, the telegraph transmitting apparatus of- Fig. l at the distant point and the telegraph receiving apparatus of Fig. 3 at the near end, as shown, will be in operation.

In general, speech over channel 2 3i enters the hybrid coil 256 provided withthe usual balancing network 2e? passes over path 288 through the network 269 to the voice operated gain adjusting device (termed vogad, for short) 2 H. From the vogad 2H speech currents enter the hybrid coil 2l2 where they split, part going on to the main speech channel and part entering the syllabi'c amplifier-detector 213 for control purposes. The output of the amplifier-detector 2 i3" feeds into the transmitting chain 2! which performs a variety of switching functions, as will be more clearly set forth hereinafter. At present it is sufficient to say that the transmitting chain 2M clears the way for the speech currents to the antenna 263 and that the distant receiving terminal similarly conditions the receiving circuits thereat for the proper reception of the speech currents. The main portion of the speech currents then passes from the hybrid coil 212 into the delay circuit 2l5 through a repeater 2:6 and the first transmitting suppressor 2H. Thereafter the speech path is through privacy circuit 2l8, the second transmitting suppressor circuit 2H9 and another part of the privacy circuit 226 to the hybrid coil 22!. The speech currents then pass to the hybrid coil 222., thence to the transmitting repeater 223 and to the radio transmitter 282.

At the distant receiving end the speech currents transmitted from the radio receiver pass through the receiving repeater 22 into the hybrid coil 225; At this point the control tone which accompanies speech is diverted to the control tone filter 226 to the receiving detector 221 which operates the receiving chain 223. This receiving chain responds to the control tone transmitted from the distant end through the operation of the transmitting chain 214 thereat and, like the transmitting chain, performs a variety of switching functions which will be more fully described hereinafter. At present it is sufficient to say that the receiving chain clears the way for the speech currents to reach the hybrid coil 206 and the channel 2!". The speech currents leaving the hybrid coil 225 enter the next hybrid coil- 229 and thence pass through a part of the privacy circuit 23$, the first receiving suppressor 25L another part of the privacy circuit 232 to the second receiving suppressor 233, From this point the speech currents pass through the variable suppressor 234, a low-pass filter 235, a volume controller 236, a repeater 231, a network 238 and thence to the hybrid coil 2% from which they pass over the channel such as 28! at the said distant terminal.

The functions of these various pieces of apparatus are briefly as follows. The hybrid coil 2% receives voice currents from the channel 2M and transmits them out over channel 268. The hybrid. coil 2% also receives voice currents from the channel 239 and transmits them out over channel 26!. Actually the voice currents split equally to paths 238 and 239 but are prevented from passing over 239 beyond the repeater 23'! by the unidirectional characteristics of this repeater. The function of the balancing network 201 is well known. In this connection it should also be noted that each of the hybrid coils 2l2, 22!, 222, 225 and 229 is provided with an appropriate balancing network. The networks 2839 and 238- are provided. to perform certain functions necessary in commercial telephone circuits to compensate for the differences in transmission when the channel 2G! is connected to dififerent types of telephone circuits. They play no particular part in the present invention as their adjusting circuits are not shown but they are included in the schematic part of this diagram in order to render the diagram as complete as possible. The vogad 2| I is a means for adjusting the gain applied to the voice currents incoming thereto so as to provide a substantially uniform level of output. The hybrid coil 212 allows a small part of the voice currents to be taken oil to the syllabic amplifier-detector 2i3 without causing distortion in voice currents flowing from the hybrid coil 252 to the rest of the circuit. The delay circuit 2 i 5 is an arrangement by which voice currents are delayed to allow time for the transmitting chain 2M to properly perform its 2,296,362 functions before the voice currents are finally delivered to the antenna 203. Since these delay circuits entail certain loss in the transmission, amplifying means are associated therewith in the form of a repeater 2I6 which is shown as a oneway amplifying repeater. The first transmitting suppressor 2H and the second transmitting suppressor 219 both act to block speech currents therethrough when the relays of the transmitting chain 2| 4 are in their normal positions. When, however, the transmitting chain is operated both transmitting suppressor 2|! and transmitting suppressor 2 ill give a clear path for the transmission of voice currents. The two privacy system units H8 and 220 are included to render the speech between the antenna 203 and the distant antenna 204 unintelligible, but do not form any essential part of the present invention, being included again for the purpose of rendering the schematic lay-out as complete as possible. The function of the hybrid coil 22I is to transmit to the hybrid coil 222 either speech coming from the privacy system unit 220 or telegraph signals coming from either the filter 250 or the filter 25!. The function of the hybrid coil 222 is to pass on to the transmitting repeater 223 both the output of the hybrid coil 22| and the control tone originating from either the oscillator 260 or the oscillator 26L These oscillators are sources of alternating current of frequencies just outside the voice range of the two twin channels explained in connection with Fig. 4 hereinbefore. These tones may be effectually filtered out at the distant receiving end without disturbing the voice currents entering the receiving channel thereat.

Current from either the oscillator 260 or the oscillator 26! enters the control tone enabler 2 which is under control of the transmitting relay chain 264, as will appear hereinafter. When the voice takes command of the transmitting chain 2M and certain relays in the telegraph transmitting apparatus of Fig. 1 are properly operated, the control tone enabler 24| will allow alternating current from either the source 260 or the source 2M to enter the control tone compressor 242 and from this point the control tone will be passed to the hybrid coil 222. The effect, therefore, is that when the voice takes command of the transmitting chain 2| 4 control tone at full volume will be delivered to the hybrid coil 222. A short time thereafter, as measured by the delay circuit 2l5 and controlled by a connection in the voice path between the first transmitting suppressor 2| 1 and the first unit of the privacy system 248, the control tone compressor will op erate to reduce the volume of the control tone being delivered to the hybrid coil 222.

The transmitting repeater 223 is a well-known type of one-Way amplifier. The radio transmitter 202 and its associated antenna 203 need no special description. Likewise, the radio receiver 205 and its associated antenna 204 need no special description. The repeater 224 is, like the repeaters 2IB and 223, a one-way amplifying device. The hybrid coil 225 receives the output of the radio receiver 205 and allows part of this output to flow to the control tone filters 220 and 243 which deliver to the receiving detector 227 only the control tone.

The hybrid coil 225 also delivers to the next hybrid coil 220 the speech currents, the accompanying control tone being filtered out later. Hybrid coil 229 acts during the transmission of speech currents to deliver the speech currents which are transmitted from the radio receiver 205 to the privacy system unit 230 and the various circuit units thereafter. During intervals of telegraph transmission the hybrid coil 229 delivers the output of the radio receiver 205 to the telegraph receiving apparatus of Fig. 3.

The privacy system units 230 and 232 are used in complement with the privacy system units 220 and 218 to insure secrecy in the transmission of intelligence by translating for delivery to channel 20I the otherwise unintelligible transmission from the antenna 203 to the antenna 204. The first receiving suppressor 23! and the second receiving suppressor 223 both operate under control of the receiving relay chain 228 to block the speech path during those intervals when the control tone is absent from the transmission being received by the receiver 205. When control tone is present as an indication that speech is present, the receiving relay chain 228 is operated and the receiving suppressors 23! and 233 give a clear path for speech currents toward the hybrid coil 206 and the channel 20L The variable suppressor 234 is a device used to cause the transition from speech to silence and from silence to speech to be slow sothat static and extraneous noises will not be applied to and removed from the speech circuit abruptly and so disturb the listener. The low-pass filter 235 effectively blocks any control tone which may have accompanied speech to this point and allows only the speech to go into the volume controller 236. At this point it should be noted that between the low-pass filter 235 and the volume controller 236 there is a connection to the receiving detector 221. Thus when the voice takes command at the distant transmitting end, control tone from one of the oscillators 260 or 26] is transmitted by the radio transmitter at full volume and this will enter the control tone filters 226 and 243 and the receiving detector 221 to insure the proper operation of the receiving master relay within the receiving chain 228. By the time that the voice arrives the receiving chain will have conditioned the receiving circuit, particularly by operating the first and second receiving suppressors 23! and 233 and the vari able suppressor 234. As the control tone is reduced in volume through the action of the control tone compressor 242 or through selective fading in the radio path, voice currents from the connection between the low-pass filter 235 and the volume controller 236 will reach the receiving detector 221 to augment the operation of this device and insure the proper and continuous operation of the receiving chain even during periods when fading or other disturbances in the mutable link cause the received control tone to drop out.

That part of the circuit between and including radio transmitter 202 and radio receiver 205 is spoken of as a mutable link since it comprises a signaling channel capable of or liable to change from internal or external noise which may give rise to interfering energy or, more specifically, subject to noise, fading or change of attenuation. It is to be understood, however, that the present showing is by Way of example and that the term mutable link does not necessarily mean that a space radio link is invariably involved but that the term is broader in its meaning and includes any channel liable to change from internal or external noise.

The volume controller 236 is a device, generally under the supervision of a technical operator,

for controlling the volume as indicated by a monitoring device (not shown) connected betweenthis unit and the receiving repeater 231. The receiving repeater 231 is, like the other repeaters 2H5, 223 and 224, a one-way amplifying device.

The syllabic amplifier-detector 2I3 is a device designed to be unoperated by the maximum noise which may be expected on the transmitting circuit but it will be operated quickly by speech signals of both high and low amplitudes. It is connected to the hybrid coil 2I2 and delivers its output to the receiving chain 2 I4. If the receiving chain 228 is idle, then the amplifierdetector 2I3 will be enabled. If at this time voice currents come in over channel 20I their effect will be to operate the amplifier-detector M3 and. thereupon to operate the transmitting relay chain 2M. The transmitting chain 254 comprises a number of relays which therefore effectually respond. to speech. Various lines from the rectangle designated 2M indicate control which this chain has over these other pieces of apparatus. For instance, the transmitting chain has control over the transmitting suppressor 2 II, the privacy control unit 2 I8 and the transmitting suppressor 2I-9. The transmitting relay shown also has control over the telegraph transmitting apparatus shown in Fig. 1. When the voice takes command and the transmitting chain 2M is operated, a ground connection will be extended by the transmitting chain 2H3 to the back contact and armature of relay I00, thence through the resistance IOI, the winding of relay I02 and the winding of relay I03 to battery. The operation of relays I02 and I03 effectively disables the transmitting telegraph apparatus. The transmitting ohain 2M also controls the control tone enabler 241 but this circuit extends through the armature and back contact of relay I04 in the telegraph transmitting circuit so that if the voice takes command at a particular time when relay I04 is operated, the transmission of control tone from either the oscillator 290 or the oscillator 20I will be delayed.

In like manner, the receiving relay chain 228 has control over various circuit units. For instance, the receiving suppressor 233 and the variable suppressor 234 are controlled by this circuit. When the receiving chain 228 is operated then the amplifier-detector 2I3 is disabled and a control exercised over the vogad ZII to maintain the gain of this apparatus at the point last set. Another line from the receiving chain 223 indicates control exercised over the telegrad 300 by the receiving chain, whereby the telegrad is rendered efiective during the periods that the chain 228 is in its normal, unoperated position.

A key 251 controls the transmission and recciving circuits for the spread and unspread conditions. In its normal position, as shown, key 251 causes the lighting of signal lamp 253, indicating the unspread condition. In this condition battery is connected to conductor 259 but conductor 258 is open, and therefore, no one of the relays 255, 253, 262, 205 or 350, connected to these conductors, is operated. With relay 255 unoperated an alternating current of a frequency of 2295 cycles from the oscillator 253 is connected to the signal converter 252. Likewise, with relay 256 unoperated the signal converter 252 is connected through the filter 250 adapted to pass alternating current of 2295 cycles to the hybrid coil 22I. With relay 262 unoperated the oscillator 260 will deliver analternating current of 3000 cycles to the control tone enabler 24I. With relay'255 unoperated control tone filter 243 tunedto 3000 cycles is connected todetector 221. With relay 350 unoperated, hybrid coil 229 is connected, through filter 30I, to the telegrad 300 and so will pass signals of a frequency of 2295 cycles.

When the key 251 is operated the signal lamp 253 is extinguished and signal lamp 264 is illuminated, thus indicating the spread condition. Key 251 also connects ground to conductor 258, resulting in the operation of relays 255, 256, 262, 265 and 350. At this time a tone source 254, delivering an alternating current of 4590 cycles, is connected to the signal converter 252. Likewise, the signal converter 252 is, through the operation of relay 250, connected through the filter 25I which will pass signals of 4590 cycles to the hybrid coil 22L With relay 262 operated the oscillator 26I, delivering an alternating current of 5250 cycles, is connected to the control tone enabler 24L Through the operation of relay 255 the control tone filter tuned to 5250 cycles is now connected to detector 221. Through the operation of relay 350 the hybrid coil 229 is connected, through filter 349, which will pass signals of 4590 cycles, to the telegrad 300.

The key 251 is under control of the technical operator at this terminal and both the key 251 at this terminal and at the similar distant terminal will be operated simulaneously under proper instructions given to the technical operators thereat.

The transmitting telegraph apparatus consists, generally, of a pair of tape transmitters I05 and I06. Each of these transmitters has a series of five contacts operating between a spacing battery lead I01 and a marking battery lead I08 and afiecting, in turn, the segments I I I to I20, inclusive, of the multiplex distributor. This latter piece of apparatus consists, in general, of a motor and synchronizing equipment III) operating a shaft I09. This. shaft has upon it a number of brushes I2I, I22, I23 and I24. The brush I2I as it passes successively over the segments III to I20, inclusive, connects these segments to the ring I25 which is connected A through either the armature and back contact of relay I26 or the armature and back contact of relay I2'I. Thence through the back contact and armature of relay I03 and the winding of the telegraph transmitting line relay I28 to a point on a potentiometer consisting of the resistances I29 and I30 whereby the relay I28 will respond to either marking or spacing potential and thus operate its armature accordingly. When relay I28 is operated by a spacing signal it closes a circuit through its armature and contact to render the signal converter 252 inefiective to transmit telegraph tone from either the source 253 or the source 254 to the hybrid coil 22I. When the relay I28 is operated by a marking signal it opens this circuit which controls the signal converter 252 in such a way that alternating current from the source. 253.0r the source 254 freely passes to the hybrid coil 22I and thence out over the radio transmitter 202.

It should be noted that when the transmitting relay chain 2M is operated and, consequently, relay I03 is operated, that a connection is extended from spacing battery lead I81 through the front contact and armature of relay I03 to the Winding of relay I28 to hold this relay spacing and, therefore, continuously to block the transmission of telegraph tone. to the hybrid coil 22I.

The function of brush I22 is as follows: If the transmitting chain operates at any time before brush I22 comes in contact with segment I33 or segment I34, then relays I02 and I03 will be properly operated and further transmission of telegraph signals interrupted and the stepping of the tape magnet prevented. If, however, the operation of the transmitting chain 2I4 occurs while brush I22 is on either ofthese segments I33 or I34, a connection will be extended from battery, ring I35 over brushvI22 to segment I33 and thence through the windings of relays I04 and I00, the back contact and armature of relay I02 to ground. This causes the circuit for the operation of relays I02 and I03 to be opened to prevent the disabling of the telegraph apparatus for this very short interval. This arrangement is provided so that if the voice takes command of the circuit at or during the transmission of the last pulse of a. telegraph code, this last pulse may be allowed to be transmitted without interruption.

The function of brush I23 is as follows: The segments and rings of this multiplex distributor are developed for the sake of clarity and the brush I23, now moving downwardly, has reached the point where transmission of the signals from the tape transmitter I06 has been completed. Brush I23 now establishes a connection from ground, ring I36, brush I23, segment I31, back contact and outer right-hand armature of relay I33, winding of stepping magnet I39, right-hand contact and armature of relay I40 to battery. If relay I40 is on its right-hand contact, as it should be while this apparatus is operating normally, and there is a suflicient supply of tape for use by the transmitter I06, then the magnet I39 will operate and advance the tape to the next punched character. As brush I23 advances it next comes into contact with segment I4I where a connection is established from ground, ring I36, brush I23, segment I4I, the contacts of the taut tape switch I42, which will be closed as long as there is sufficient tape in this transmitter, to the left-hand winding of relay I38. This connection also extends in parallel through the normal contacts and the inner right-hand armature of relay I38 through the right-hand winding of this relay, and these windings being opposed no operation of the relay I38 will occur. If, however, upon the operation of magnet I39 the taut tape switch I42 had operated, then only the righthand winding of relay I38 would have been energized and this relay would then have operated and looked through its inner right-hand armature to ground. This condition would have persisted until the taut tape switch I42 closed its contacts again and brush I23 made contact with segment I4I whereupon the relay I38 would have been automatically released.

During the time that relay I38 is operated, each of th segments II6 to I20, inclusive, would have been connected through the front contacts and left-hand armatures of relay I38 to marking battery so that a signal consisting of five marking pulses would have been repeatedly sent each time the brush I25 passed over the segments II6 to I20, inclusive.

When brush I23 advances to segment I43 a connection is momentarily established from ground, ring I36, brush I23, segment I43, the lower winding of relay I40 to battery. This tends to drive relay I40 to its right-hand contact where it will remain unless some other circuit is closed to change this condition.

As brush I23 advances further it first causes the operation of stepping magnet I44 in a similar manner to the operation of stepping magnet I39 and attempts to operate the relay I45 and finally closes a circuit to drive relay I43 to its right-hand armature.

The function of brush I24 is as follows: If during the time that brush I24 is on segment I41 relay I02 becomesoperated, then a circuit will be established from ground, the armature and front contact of relay I02, ring I48, brush I24, segment I41, the upper winding of relay I43 to battery. Relay I46 will thereupon be driven to its left-hand contact where it will remain until brush I23 drives it back to its left-hand contact. During the time that relay I46 is on its left-hand contact it will cause the operation of relay I23 in an obvious circuit and thereby open the transmitting circuit which operates the telegraph transmitting relay I28. When brush I24 reaches the lower segment I49 it will cause the relay I40 to move to its left-hand contact whereupon the relay I21 will be operated and complete the opening of the circuit for relay I28. It will be noted that each of these relays I46 and I40 will be periodically returned to its righthand contact at the ending of the period of activity of the other circuit but if the telegraph transmitting apparatus is now rendered ineffective, the relay will return to its left-hand contact immediately thereafter and before any'signals can be effectively transmitted.

It should be noted before leaving the descrip-' tion of the transmitting telegraph apparatus that if both the taut tape switches open the lefthand windings of relays I38 and I45, respec tively, that the contacts and the left-hand armatures of relay I45 are connected to spacing battery so that first a series of five marking impulses and later a series of five spacing impulses will be transmitted. This provides for a repeating transition between five spacing and five marking impulses for the purpose of correcting the distributor speed at the distant end.

When the receiving relay chain 228 is in its normal unoperated condition, then the telegrad 300 will be enabled. This will render the telegrad eifective to operate the receiving telegraph apparatus. At this time telegraph signals being received by the radio receiver are passed into hybrid coil 229 and thence into the band-pass filter 30I or band-pass filter 343 from which they are delivered to the telegrad 300. This results in the operation of relays 302, 333 and 334 to their marking contacts for each marking impulse delivered to the telegrad 300. Relay 332 is known as the receiving telegraph line relay and for each marking impulse it establishes a ground connection to the ring 305. Relay 334 is known as the correotor relay. Upon each spacing impulse this relay will cause its condenser 303 to be energized and upon each marking impulse this relay will deliver the condenser discharge into ring 301. Relay 303 is known as the auxiliary relay and operates on each marking impulse to drive either relay 308 or relay 309 to its left-hand contact, respectively.

The receiving telegraph apparatus consists, generally, of two printers 3I0 and 3| I and a multiplex distributor comprising a motor and certain synchronous equipment 3 I 2 operating a shaft 3I3 carrying brushes 3I4, 3I5, 3I6 and 3H.

As brush 3I4 moves downwardly it connects tended to ground on ring 330.

the ring 3.95 through segments 3E8, 3l9, 320, 32! and 322 to the selecting magnets of printer 3H and thereafter through segments 323, 324, 325, 326 and 321 to the selecting magnets of printer 3I9. Thus for each marking impulse one of the selecting magnets of printer 3H or printer 3H] is operated.

Brush 3H5 in moving downwardly makes contact with segments 328 and then 329 while brush 3I4 is traversing the connections to the selecting magnets of printer 3| l. The segments 328 and 329 are associated with printer 3H1. The connection to segment 328 establishes a circuit from ground, ring 330, brush 316, segment 328, armature and contact of relay 338 to the printing magnet 331. Thus the selection set up on printer 310 is rendered effective by the printing magnet 33l after the brush 314 has completely traversed the'segments 323 to 321 and is'now engaged in passing over the segments 3!!! to 322. As the brush 3l6 advances it makes a connection from ground to segment 329, which leads to the lower right-hand set of contacts of key 332, for purposes which will be hereinafter described.

As brush 3l6 next traverses segment 333 the k printing magnet 334 will be operated.

' Brush 311 makes contact from the ring 335 to the segment 336 during the time that the brush 3M is traversing the segments associated with the printer 3| I. This circuit from ring 335 extends a battery connection to the two windings of the relay 339 through the rectifiers 331 and 338. If this telegraph receiving apparatus is now properly in operative condition, there will be an open connection to the upper winding of this relay at the armature and contact of relay 339. Any marking impulse coming in at this time will be rendered eiiective by the auxiliary relay 303 to keep relay 309 on the left-hand contact and thus render the printing magnet effective. If, on the other hand, the receiving chain 228 is operated by voice currents, then relay 339 will be released and ground on the armature of relay 339 will cause relay 309 to be driven to its other position where the circuit for printing magnet 334 is opened. Similar action of relay '308 will take place when the brush 3|1 traverses the segment 34L It will also be noted that when the relay 339 is operated, as when the receiving chain 228 is in its normal position, thus denoting the fact that the receiving telegraph apparatus is effective, that relay 340 will be operated. Relay 349 plays a particular role with relation to the key If the distant transmitter corresponding to transmitter 103 operates its taut tape switch so as to send out a series of five marking impulses, then the receipt of these five marking impulses by the printer'3l0 results in a thumping of the teletypewriter apparatus without the production of any printing. If this becomes annoying to the operator, then the key 332 may be moved to its right-hand position. Thereupon a circuit will be established from battery, the upper righthand contacts of key 332, the winding of relay 3.42, the lower right-hand contacts of key 332 to the segment 329 and when brush 3L6 makes contact with segment 329 a connection is ex- This causes relay 342 to operate and this relay locks up to battery on its inner right-hand armature. Relay 342 is sufiiciently slow in releasing so that it will remain locked. up in .a manner now to be described. Upon the first operation of relay hand armature of relay 342.

342 a circuit for the operation of relay 343 is closed at the front contact and outer right- This relay now disconnects the segments 323 to 321, inclusive, from the selecting magnets of the printer 31B and extends them to conductor 344 which, with the left-hand contacts of key 332 in their normal position, extends the ground connection each time the brush 3M connects with a segment 323 to 321, inclusive, to the winding of relay 342 to maintain this relay operated.

If at the distant end the taut tape switch should return to normal, then ground impulses will not be supplied to the winding of relay 342 at sufficient intervals to keep this relay operated and it will therefore release and by releasing cause relay 343 to return to normal, so that the printer 3H] again becomes effective. If during the time that relay 342 is locked up the receiving telegraph apparatus is rendered ineffective by the operation of the receiving chain 228, then relay 343 returns to normal and this maintains relay 342 locked up until the telegraph apparatus is again rendered effective through the operation of the receiving chain 228.

The relay 342 may be unlocked at any time by moving the key 332 to its left-hand position.

As brush 3E5 moves it alternately makes contact with segments connected to either conductor These conductors are connected to difierent windings of the auxiliary-corrector relay 3'41 and therefore the discharge of the condenser 393 will tend to operate the relay 341 in one direction if the motor 3l2 is running fast or operate the relay 3'31 in the other direction if the motor 3l2 is running slow. The correcting means is well known andwill not be further described except to note that a device 348, which will indicate fast or slow operation, is inserted at this point to indicate that correction may be properly made.

'What is claimed is:

1. In a communication system, a plurality of transmission channels comprising a carrier and means for utilizing portions of the side-bands "thereof for transmission purposes, one channel including a limited band of frequencies on one side of and close to'the carrier and another channel including a different limited band of frequencies on the other side of and relatively distant from the carrier, control and signaling means for each said channel comprising sources of alternating current, one of a frequency outside the said limited band and another of a frequency within the said limited band and controlling circuit devices including filtering networks for said control, and signaling currents and switching means for alternatively rendering the said control and signaling means for either said channel efiective.

2. In a communication system wherein a first type of transmission is interpolated in a second type of transmission during lulls and pauses in saidsecond type of transmission, twin transmission channels comprising a carrier and means for utilizing portions of the side-bands thereof for transmission purposes, one of said twin channels including a limited band of frequencies. on one side of and close to the said carrier and the other of said twin channels including a difierent limited band of frequencies on the other side of and relatively distant from the said carrier, controlmeans for each said channel for said second type of transmission comprising sources of alternating current outside said limited bands of frequencies and tuned controlling devices including filtering networks corresponding thereto, signaling means for each said channel for said first type of transmission comprising sources of alternating current within said limited bands of frequencies and, tuned controlling devices including filtering networks corresponding thereto, and switching means for alternatively rendering said control and signaling means for either said channel effective.

3. In an interpolated telephone and telegraph system wherein telegraph signals are interpolated in telephone conversations during lulls and pauses therein, a twin channel transmission system comprising a carrier and means for utilizing portions of the side-bands thereof for transmission purposes, one of said twin channels including a limited band of frequencies on one side of and close to the said carrier and the other of said twin channels including a different limited band of frequencies on the other side of and relatively distant from the said carrier, interpolating control means for each said twin channel for simultaneous use with the telephone facilities of said system comprising sources of alternating current each outside the corresponding said limited band of frequencies and tuned controlling devices including filtering networks corresponding thereto, telegraph signaling means for each said twin channel for use during the lulls and pauses in the telephone conversation comprising sources of alternating current each within the corresponding said limited band of frequencies and tuned controlling devices including filtering networks corresponding thereto, and switching means for alternatively rendering said control and said signaling means for either said channel effective.

4. In an interpolated telephone and telegraph system wherein telegraph signals are interpolated in telephone conversations during lulls and pauses therein, a terminal comprising transmitting and receiving means, transmission channels for associating said transmitting apparatus with distant receiving apparatus and said receiving apparatus with distant transmitting apparatus, each said transmission channel comprising a twin channel transmission system comprising a carrier and means for utilizing portions of the side-bands thereof for transmission purposes, one of said twin channels including a limited band of frequencies' on one side of and close to the said carrier and the other of said twin channels including a different limited band of frequencies on the other side of and relatively distant from the said carrier, the carriers for said transmitting and receiving channels of said terminal being different and the frequency characteristics of said twin channel side-band channels being alike, interpolating control means for each said twin channel for simultaneous use with the telephone facilities of said system comprising sources of alternating current each outside the corresponding said limited band of frequencies associated with the transmitting circuits of said terminal and tuned controlling devices including filtering networks corresponding thereto associated with the receiving circuits of said terminal, telegraph signaling means for each said twin channel for use during the lulls and pauses in the telephone conversation comprising sources of alternating current each within the corresponding said limited band of frequencies associated with the transmitting circuits of said terminal and tuned controlling devices including filtering networks corresponding thereto associated with the receiving circuits of said terminal, and switching means individual to said terminal for alternatively rendering said control and signaling means for either said channel effective.

5. The method of operating a system of transmission which includes means for transmitting and receiving a carrier wave modulated in accordance with a signal current and a control current which comprises at one time transmitting an essentially single side-band modulated wave in which the signal and control current are on one side of the carrier wave in the frequency spectrum and at another time transmitting an essentially single side-band modulated wave in which the signal wave and control wave are on the other side of the carrier wave in the frequency spectrum and further removed therefrom than in the first case, and changing the transmitting and receiving apparatus at intervals from one condition to the other.

6. The method of transmission with relation to the carrier frequency of an assigned channel which comprises transmitting successively under control of the same source or sources of signals to be transmitted an unspread band on one side of the carrier frequency and a spread band on the other side of the carrier frequency.

7. The method of transmitting speech having telegraph signals interpolated in the silent intervals thereof as a side-band of a carrier wave which comprises at intervals shifting speech and telegraph signals from one side-band of the carrier wave to the other and shifting a receiving apparatus correspondingly at the same time.

8. In a carrier wave transmission system in which signal waves of a special class are accompanied lay a convoy current, means for transmitting the convoy current at one time as one sideband of a carrier wave and at another time as the other side-band of the same carrier wave.

9. In a system of carrier wave communication in which a special signal is transmitted with a convoy current, means for shifting the convoy current from one side to the other of a modulated carrier wave and simultaneously shifting the wave representing the special signal from one side to the other of the carrier wave.

ALFRED E. MELHOSE. 

